Study of lithium ion intercalation/de-intercalation into LiNi1/3Mn1/3Co1/3O2 in aqueous solution using electrochemical impedance spectroscopy

Abstract

The mechanism of lithium ion intercalation/de-intercalation into LiNi1/3Mn1/3Co1/3O2 cathode material prepared by reactions under autogenic pressure at elevated temperatures method is investigated both in aqueous and non-aqueous electrolytes using electrochemical impedance spectroscopy (EIS) technique. In accordance with the results obtained an equivalent circuit is used to fit the impedance spectra. The kinetic parameters of intercalation/de-intercalation processes are evaluated with the help of the same equivalent circuit. The dependence of charge transfer resistance (R ct), exchange current (I 0), double layer capacitance (C dl), Warburg resistance (Z w), and chemical diffusion coefficient (D Li+) on potential during intercalation/de-intercalation is studied. The behavior of EIS spectra and its potential dependence is studied to get the kinetics of the mechanism of intercalation/de-intercalation processes, which cannot be obtained from the usual electrochemical studies like cyclic voltammetry. The results indicate that intercalation and de-intercalation of lithium ions in aqueous solution follows almost similar mechanism in non-aqueous system. D Li+ values are in the range of 10−8 to 10−14 cm2 s−1 in aqueous 5 M LiNO3 and that in non-aqueous 1 M LiAsF6/EC+DMC electrolyte is in the order of 10−12 cm2 s−1 during the intercalation/de-intercalation processes. A typical cell LiTi2 (PO4)3/5 M LiNO3/LiNi1/3Mn1/3Co1/3O2 is constructed and the cycling stability is compared to that with an organic electrolyte.